The Peltier effect is a thermoelectric effect demonstrated by reference to FIG. 1 (prior art) showing a thermocouple of two dissimilar conductors, 10 and 12, joined at one junction 14 maintained at temperature T' by reservoir 18 and joined at a second junction 16 maintained at a lower temperature T" by reservoir 20. If conductor 10 is broken and a motor 22 is connected to the thermocouple, then an electric current I will flow through each conductor and a back EMF (E) across the motor terminals will be generated such that EQU EI=.PI.'I-.PI."I
EI is the work performed by the motor 22. .PI.I represents heat from reservoir 18 flowing into the thermocouple at the first junction 14 and .PI."I represents heat flowing into reservoir 20 out of junction 16. The "Peltier" coefficients .PI.' and .PI." have values characteristic of the materials at temperatures T' and T" respectively. The Peltier coefficient of each junction is a function of temperature governed by: EQU .PI./T=dE/dT.
Factors which diminish the efficiency of the thermoelectric power generator of FIG. 1 include joule heating and the Thompson effect. The Thompson effect is the efflux or influx of heat in a conductor conducting an electric current simultaneously with the presence of a thermal gradient in the conductor. In the foregoing discussion, the Thompson effect has been neglected.
Another important factor that limits the efficiency of the thermoelectric power generator of FIG. 1 is the rate with which the reservoir 18 supplies heat to the junction 14 and the rate with which junction 16 supplies heat to reservoir 20. This rate can be limited, for example, by thermal conductivities of the media of reservoirs 18 and 20 which reduce the thermal gradient between junctions 14 and 16. Another consideration is that, while a large thermal gradient between the junctions generates a greater Peltier potential, it also results in increased heat being conducted through the junction and dissipated by the heat sink.
The net effect of factors leading to thermal losses is that, as the temperature difference across the thermoelement is increased, the advantage of increased thermopotential due to the increased difference of work functions is offset by a greater increase of thermal losses due to, for example, photon and phonon vibrations, etc.
According to the present state of the art, the most efficient thermoelectric materials are semiconductors such as lead telluride, silver gallium telluride, copper gallium telluride, silver indium Telluride, silver gallium telluride, copper gallium telluride, sodium manganese telluride. Compounds of Selenium, for example silver antimony Selenide and of sulfur, for example, the rare earth sulfides, exhibit strong thermoelectric properties. Compounds containing at least one member of the group selenium, sulfur and tellurium are known as chalcogenides. Small amounts of various agents (doping agents) such as indium or sodium may be incorporated in the thermoelectric compositions to establish the type of conductivity (p or n) of the material) The most commercially common pn materials used for electrical power generation are either Bismuth Telluride or Lead Telluride.
Those materials which are the primary materials used to generate electrical power according to the present state of the art, all have poor Carnot efficiencies. in converting fuel into electricity. The Carnot efficiency of present thermoelectric materials in commercial electrical generation systems as a whole never exceed 6%. (Some manufacturers claim 8-9% for n type lead telluride but this claim is not a system claim but a claim for a single material standing alone.) because of the low Carnot efficiency, thermoelectric devices are not employed for generating electricity for utility purposes.
Thermoelectric generation of power using p n materials is generally employed only under conditions where reliability is a greater concern than energy efficiency. A typical commercial bismuth telluride electrical generator has a thermopile between a gas driven burner and a set of cooling fins exposed to ambient temperature. The temperature of gas (air) carrying exhaust heat emitted from a well designed commercial thermoelectric generator is ideally very near the temperature of the cooling fins. Nevertheless, the present state of the art generator is characterized by substantial loss of heat such that the efficiency is about 6%.
According to practices of the present art, heat generated by thermoelectric devices that was not used to generate thermoelectricity was either used directly for such purposes as to heat water or a room or was wastefully exhausted.
For example, some manufacturers of hot water heaters have placed a thermopile (generally thermal piles made of bismuth telluride) between a heat source (produced by a flame) and the water that is to be heated. This was an attempt to use all the heat to warm water that was not used to produce thermoelectricity.
The principle of the Carnot cycle which applies to the devices discussed above is to extract energy as heat, Q.sub.2, from a source at a temperature T.sub.2, apply a a portion of the energy to performance of work, W, and discharge the remainder, Q.sub.1 =Q.sub.2 -W at a lower temperature. T.sub.1. According to the well known Carnot principle, the maximum efficiency, E=W/Q.sub.2 that can be achieved from a carnot engine operating between temperatures T.sub.1 and T.sub.2, is:: EQU E.sub.max =(T.sub.2 -T.sub.1)/T.sub.2 (The Carnot efficiency)
The objective in operating a refrigerator is to perform work to withdraw heat Q.sub.2 ' from a source at temperature T.sub.2 ' and to discharge the heat Q.sub.2 ' to a heat sink at temperature T.sub.1 ' where T.sub.1 &gt;T.sub.2. This requires performing an amount of work W which is equivalent to an additional amount of heat discharged to the heat sink so that the total amount of work discharged to the heat sink is Q.sub.1 ' where: EQU Q.sub.1 =Q.sub.2 +W
A typical absorption refrigerator system circulates a solution containing two components which have different boiling points. A common solution for this type of refrigeration is ammonia dissolved in water. A gas flame heats the solution of ammoniated water to chive off gaseous ammonia. The ammonia gas is then cooled in a condenser to ambient temperature and condenses to a liquid. The heat of condensation is expelled to the ambient environment. The liquid ammonia is then discharged into an evaporator where it evaporates and therefore absorbs heat so as to produce a cooling effect. Hydrogen gas is present in the evaporator and mixes with the ammonia thereby ballasting the pressure throughout the system. The heavy ammonia vapor mixed with hydrogen is then conducted to an "absorber" where the ammonia is absorbed by incoming water and the hydrogen is expelled. The ammonia dissolving in the water generates heat and this heat of solution is allowed to dissipate from the absorber in order to maintain the temperature of the water ammonia solution at ambient temperature and ensure that the water is saturated with ammonia at room temperature. Then the ammonia-in-water solution circulates back to the location of the flame where ammonia is driven off by the heat of the flame and the cycle is repeated. For a more detailed description of the absorption refrigerator, the reader is referred to "Heat and Thermodynamics" by Zemansky published by McGraw Hill, New York, N.Y. 1943 pages 211-214 which is hereby incorporated as reference into this specification.
All of the generating and refrigerating devices of the present art described above discharge large amounts of waste heat.